The present invention generally relates to an AC driving type of display apparatus such as matrix type of liquid crystal display apparatus or the like.
FIG. 7 shows a circuit diagram showing an equivalent circuit of a liquid crystal panel in a liquid crystal display apparatus of an active matrix driving system. Referring to FIG. 7, picture elements Q are arranged respectively in the respective cross positions among a plurality of row electrodes X1, X2, X3, X4, X5 (hereinafter the optional row electrode is shown with a reference character X) arranged in parallel to one another, and a plurality of column electrodes Y1, Y2, Y3, Y4, Y5 (hereinafter the optional column electrode is shown with a reference character Y) arranged in parallel to one another which are orthogonal with respect to the row electrodes X1 through X5. Further the respective picture elements Q are connected with the corresponding column electrodes Y through the switching elements K, and the control terminals of the respective switching elements K are connected with the corresponding row electrodes X.
FIG. 8 is a wave-form chart showing one example of the driving wave forms of the liquid crystal pulses. With reference to the wave-form chart, the driving operation of a picture element Q1i, which is located in the cross position between the row electrode X1 and the column electrode Yi (i=1 through 5) in FIG. 7, will be described hereinafter.
The scanning pulses G1 through G5 are applied sequentially in line respectively upon the respective row electrodes X1 through X5 of the liquid crystal pulse of FIG. 7 as shown in FIG. 8 (1) through (5), with a result that the switching elements K connected with the respective row electrodes X1 through X5 are on, sequentially, one line by one line.
A signal voltage Si to be stored in each picture element corresponding to the column electrode Yi is applied upon the column electrode Yi through the switching element K, as shown in FIG. 8 (6), in the synchronous operation with the scanning pulses G1 through G5.
With the observation of the switching element K connected with a first row electrode X1, the signal voltage Si to be applied upon the column electrode Yi is v1 in a period T1 where the switching element K becomes on with the scanning pulse G1, so that the voltage v1 is stored in the picture element Q1i. Also, since the switching element K becomes off at the periods T2 through T5 after the period T1, the voltage v1 previously stored is retained by the liquid crystal capacity of the picture element Q1i during this period. Namely, the applied voltage V1i onto the picture element Q1i is retained as shown in FIG. 8 (7) during the period T1 through T5. At the period T1' when the application of the scanning pulses G1 through G5 onto all the row electrodes X1 through X5 takes a round, then the switching element K connected with the row electrode X1 becomes on again with the scanning pulse G1, the signal voltage Si to be applied upon the column electrode Yi becomes a voltage -V1 opposite in polarity to a case of the period T1, and the voltage -V1 is stored in the picture element Q1i. At the periods T2' through T5' after the period T1', the switching element K becomes off. The applied voltage V1i into the picture element Q1i is maintained into -V1 as shown in FIG. 8 (7) during this period. In this manner, the applied voltage V1i into the picture element Q1i becomes opposite in polarity between a first field F1 of the period T1 through T5 and a second field F2 of the periods T1' through T5', so that the AC rectangular waves are applied upon the picture element Q1i during the period.
As described hereinabove, in the liquid crystal display apparatus of such active matrix driving system, an AC driving operation which inverts, for each of the fields, the polarity of the signal voltage to be applied upon the respective column electrodes Y1 through Y5. This operation prevents the application of the DC voltage upon the liquid crystal, which causes the display quality to be lowered, the crystal to be deteriorated, and so on.
In such a crystal display apparatus as described hereinabove, in order to display the images of, for example, the television broadcasting operation, it is necessary in the above described AC driving operation that the picture signals in the odd-number fields should be in complete conformity with the picture signals at the even-number fields. In the case of the normal television picture signals, it is infrequent that the picture signals of the respective fields are in complete conformity, and it is often the case that the picture signals have fairly strong interrelation among the respective fields, so that the AC driving operation is not largely interfered with.
But when the television images transcribed by, for example, a video tape recorder are displayed, the picture signals of the odd-number fields are extremely different from the picture signals of the even-number fields because of the inconveniences of the reproduction head. Thus, the above described AC driving operation is considerably interfered with. Thus, there is a problem that the display quality is lowered and the liquid crystal is deteriorated.